Method and system for forming a patterned metal film on a substrate

ABSTRACT

A method and system for forming a thin patterned metal film on a substrate are presented. The method includes applying an ink composition on a pre-treated surface of the substrate, wherein the ink composition includes at least metal cations; and exposing at least the applied ink composition on the substrate to a low-energy plasma, wherein the low-energy plasma is operated according to a first set of exposure parameters.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of PCT application No. PCT/US2015/056435, filed on Oct. 20, 2015, which claims the benefit of U.S. Provisional Application No. 62/066,392 filed on Oct. 21, 2014, the contents of which are hereby incorporated by reference.

TECHNICAL FIELD

The present disclosure relates generally to techniques and an ink composition for forming conductive material on substrates, and in particular to techniques for fabricating or printing thin patterned metal films on substrates.

BACKGROUND

The field of organic and printed flexible electronic devices is a fast growing field with a wide range of applications in the fields of light emission, light-energy conversion, microelectronics, and macro electronics. For example, organic field-effect transistors (OFETs) and organic light-emitting diodes (OLEDs) have garnered great interest due to their technological potential as a cheap alternative to inorganic, e.g. silicon-based, thin-film transistors and diodes. Further, organic electronics may provide electronic circuits with new attractive properties, such as flexibility and transparency. The structure of an organic electronic device may include a single layer or multiple layers of organic materials and patterned metal features (e.g., electrodes). However, the formation of electrical contacts with the organic layers has not yet matured to an efficient industrial fabrication process. This is due mainly to the cost, materials, and fabrication techniques that are being used.

Specifically, utilization of organic materials in electronic devices or circuits places certain restrictions on the fabrication processes which ultimately limit the functionality of the resulting fabricated organic electronic devices. This is due to the low decomposition temperature of organic compounds as well as their relatively high susceptibility to undesired chemical reactions that destroy their functionality arising during fabrication.

The physical vapor deposition (PVD) technique is one of the fabrication techniques utilized for forming metal electrodes with organic layers. The PVD technique uses a physical process, such as heating or sputtering, to produce a vapor of material, which is then deposited on the object which requires coating. The PVD process is typically used in the manufacture of items which require thin films for mechanical, chemical or electronic reasons. Examples include semiconductor devices such as thin film solar panels.

The PVD process is mainly based on vapor deposition approaches that are prone to damaging the organic active components. For example, when the PVD method is utilized, the metal material is evaporated from a solid source onto a substrate located at a certain distance from the source. Further, when the PVD is utilized, the whole process is performed in a vacuum chamber. During the process, high-energy metal atoms “bombard” the substrate surface and are able to penetrate into organic materials, thereby substantially damaging the organic surface. The damage and the loss of the evaporated metal associated with the use of the PVD process limits the cost efficiency of the PVD method for preparing organic electronic devices.

Another fabrication technique utilized for forming metal electrodes organic layers is chemical vapor deposition (CVD). During a CVD fabrication process, the organic substrate is exposed to highly reactive and aggressive reagents in the reaction chamber which are harmful to the organic substrates.

Other techniques for forming metal films on substrates include inkjet printing, screen printing, aerosol printing, and nanoimprint lithography, all of which use nanoparticle dispersion. In most implementations, the “ink” used in these printing processes is based on organic-ligand stabilized dispersions of metal nanoparticles or metal organic compounds. The ink-based printing of metal films can be integrated in large-scale manufacturing systems for electronic devices. However, existing ink-based printing processes are very expensive due to the cost of such ink compositions. Specifically, the manufacturing of the ink is expensive because of the number of processing steps associated with synthesis, dispersion, purification, and concentration of the ink solution. Further, using currently available ink solutions requires heating of the solution when applied on the substrate in order to form the film.

For example, an ink composition for printing on a ceramic substrate utilized in existing solutions includes in part sub-micron particles acting as a binding composition and having a melting point below 600° C. Such a binding composition becomes an integral part of the substrate upon exposure to temperatures above the melting point of the binding composition.

It would therefore be advantageous to provide a method, system and an ink composition for forming a patterned metal film on a substrate that would overcome the deficiencies of the prior art.

SUMMARY

A summary of several example embodiments of the disclosure follows. This summary is provided for the convenience of the reader to provide a basic understanding of such embodiments and does not wholly define the breadth of the disclosure. This summary is not an extensive overview of all contemplated embodiments, and is intended to neither identify key or critical elements of all embodiments nor to delineate the scope of any or all aspects. Its sole purpose is to present some concepts of one or more embodiments in a simplified form as a prelude to the more detailed description that is presented later. For convenience, the term “some embodiments” may be used herein to refer to a single embodiment or multiple embodiments of the disclosure.

The disclosed embodiments include a method for forming a thin patterned metal film on a substrate. The method comprises applying an ink composition on a pre-treated surface of the substrate, wherein the ink composition includes at least metal cations; and exposing at least the applied ink composition on the substrate to a low-energy plasma, wherein the low-energy plasma is operated according to a first set of exposure parameters.

The disclosed embodiments also include a machine for forming a thin patterned metal film on a substrate. The machine comprises a container adapted to contain an ink composition, wherein the ink composition includes at least metal cations; a nozzle adapted to apply the ink composition on a pre-treated surface of the substrate; a plasma applicator adapted to expose at least the ink composition applied on the substrate to a low-energy plasma operated according to a first set of exposure parameters; and a controller configured to control the operation of the nozzle and the plasma applicator.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter disclosed herein is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other objects, features, and advantages of the disclosed embodiments will be apparent from the following detailed description taken in conjunction with the accompanying drawings.

FIG. 1a through 1e are diagrams illustrating the process of forming a thin patterned metal film on a substrate according to an embodiment

FIG. 2 is a flowchart illustrating a method for forming thin patterned metal films on substrates using plasma according to an embodiment

FIG. 3 is a block diagram of a machine structured to form thin patterned metal films on substrates according to the various embodiments disclosed herein.

FIG. 4 is a scanning electron microscope (SEM) image of a silver metal film formed on a silicon substrate formed according to an embodiment.

FIG. 5 is a SEM image of a gold metal film formed on a PET substrate formed according to an embodiment.

DETAILED DESCRIPTION

It is important to note that the embodiments disclosed herein are only examples of the many advantageous uses of the innovative teachings herein. In general, statements made in the specification of the present application do not necessarily limit any of the various claimed embodiments. Moreover, some statements may apply to some inventive features but not to others. In general, unless otherwise indicated, singular elements may be in plural and vice versa with no loss of generality. In the drawings, like numerals refer to like parts through several views.

According to the disclosed embodiments, an ink composition, a machine, and a process for forming thin patterned metal films on a substrate are disclosed. The process for forming the metal films may be any fabrication, manufacturing, and/or printing process. The disclosed process is based, in part, on exposing a substrate having portions thereof coated with the ink composition to plasma for a predefined period of time.

The plasma is low energy plasma, such as radio frequency (RF) plasma or another non-thermal plasma. The use of low energy plasma enables the conduction of a chemical reaction without creating high temperatures on the surface of the substrate. Thus, the disclosed process would not damage or otherwise harm the surface or deeper layers of the substrate. It should be noted that the metal film includes any metal feature that can be adhered or bounded to the film. Furthermore, “metal” of the metal film as referred to herein includes any metals, metal alloys, and/or mixtures of various types of metals.

The patterned metal features may be electrodes or any passive electrical element.

Therefore, the forming process and ink composition disclosed herein allows for low-cost and mass-manufacturing of electronic devices including, but not limited to, frequency identification tags (RFIDs), electronic sensors, integrated electronic circuits, flexible displays, photovoltaic devices, organic field effect transistors (OTFTs or OFETs), organic light emitting diodes (OLEDs), and the like.

FIGS. 1a through 1e are exemplary and non-limiting diagrams illustrating a process of forming a thin patterned metal film on a substrate according to an embodiment. Referring to FIG. 1a , the process is performed over a substrate 110. The substrate 110 can be made of materials including, but not limited to, organic materials, ceramic, silicon, glass, cellulose nanofibers, and the like. In addition, the substrate 110 may be made of materials sensitive to high temperatures such as, but not limited to, polyethylene terephthalate (PET), polyimide, polyethylene naphthalate (PEN), and the like. Such substrates are typically in a form of films or sheets. In an embodiment, the substrate 110 may be prepared solely from organic materials, solely from inorganic materials, or from a combination or hybrid of organic and inorganic materials.

In an embodiment, prior to film formation, the substrate 110 may optionally be first cleaned using a proper procedure for cleaning substrates. In an exemplary embodiment, a sonication cleaning procedure using a cleaning solution (such as, e.g., Isopropyl alcohol) can be utilized. It should be noted that other cleaning procedures may be utilized without departing from the scope of the disclosed embodiments. One of ordinary skill should be familiar with other cleaning procedures that can be used for this purpose.

The substrate 110 is treated so only desired areas of the surface of the substrate 110 will react with, or be exposed to, an ink composition, when such composition is applied. The desired areas include one or more patterns where the patterned metal film(s) will be formed. In certain implementation, a mask is first placed on the substrate's surface to mark the desired areas. Such a mask can be further used when applying the ink composition on the substrate. In an embodiment, such treatment is performed by exposing the substrate 110 to a low-energy and non-thermal plasma, such as Oxygen plasma. To this end, the substrate 110 is placed in a first chamber 101 and exposed to Oxygen plasma in a first exposure as determined by a first set of exposure parameters including, for example, power, RF frequency, gas flow rate, and time duration. The values of the first set of exposure parameters are determined based, in part, on the type of the substrate 110.

In certain embodiments, an atmospheric plasma (e.g., of Oxygen) is utilized. Exposing the substrate to the atmospheric plasma can be performed using an atmospheric plasma jet, an atmospheric plasma spray, a dielectric barrier discharge, and the like. Thus, in this embodiment, the chamber 101 is not required. As noted above, the low-energy and non-thermal plasma are used regardless of whether the chamber 101 is used. The temperature range of the substrate that is exposed to the plasma is between 50° C. and 70° C.

Referring to FIG. 1b , after cleaning and/or treating the substrate 110, a mask 120 is applied to create the desired pattern. The mask 120 ensures that the ink composition is applied to the substrate 110 only in the desired pattern to form the thin patterned metal film. In this example, the pattern is a rectangular stripe.

According to some embodiments, shadow masking is utilized such that a polymeric mask 120 is applied directly to the surface of the substrate 110. In such embodiments, voids (spaces) in the mask 120 define where the ink composition contacts the substrate's 110 surface. As noted above, the mask 120 can also be used for pre-treating the substrate.

Referring now to FIG. 1c , the ink composition 130 is applied on the substrate 110, specifically to areas not covered by the mask 120. In an embodiment, the ink composition 130 is applied by a means including, but not limited to, drop-casting, spin-coating, spray-coating, immersion, flexography, gravure, inkjet printing, aerosol jet printing, contact imprinting, and the like.

Referring now to Referring to FIG. 1d , the substrate 110 including the mask 120 and the ink composition 130 is placed in a second chamber 102 and exposed to plasma gas in a second exposure as determined by a second set of exposure parameters. The plasma gas utilized in the second phase in the chamber 102 includes an inert gas such as Argon, Nitrogen, and the like. The second exposure parameters include, for example, power, frequency, gas flow rate, and time duration. The values of the second set of exposure parameters are determined based, in part, on the type of the substrate 110, the ink composition 130, and/or the means of application. It should be noted that the chamber 102 may be a vacuum chamber. It should be further noted that the chambers 101 and 102 may be the same chamber such that the first and second exposures differ only in the type of gas flowing through the chamber in each phase. The mask 120 may be removed after applying the composition 130. The mask 120 may further remain for the duration of the second exposure and removed thereafter.

In certain embodiments, an atmospheric plasma of an inert gas such as, e.g., Argon or Nitrogen plasma, is utilized also during the second exposure. Exposing the substrate to the atmospheric plasma can be performed using an atmospheric plasma jet, an atmospheric plasma spray, a dielectric barrier discharge, and the like. Thus, in this embodiment, the chamber 102 is not required. As noted above, the low-energy and non-thermal plasma are being used regardless if the chamber 102 is being used. Therefore, the temperature range that the substrate is exposed to, also in this phase, is between 50° C. and 70° C.

Referring now to FIG. 1e , as a result for the exposure to the Argon or Nitrogen plasma, the substrate 110 is covered by the thin patterned metal film 140 shaped in the pattern of the mask 120. The chemical and electrical properties of the thin patterned metal material film 140 are determined based on the chemical properties of the ink composition 130 and the substrate 110 as well as based on the exposure parameters of the exposure to the Argon or Nitrogen plasma. For example, the thickness of the patterned metal film 140 can be controlled by modifying the concentration of the metal in the ink composition 130, the duration of the exposures to the plasma in the second phase, and/or the number of plasma exposure “treatments”. Additional examples for chemical and electrical properties are described further herein below.

FIG. 2 is an exemplary and non-limiting flowchart 200 illustrating a method for forming thin patterned metal films on substrates using plasma according to one embodiment. At S210, the substrate is cleaned using a cleaning procedure. The cleaning procedure is determined based on the type of substrate. At S220, the certain patterned areas of the substrate are pre-treating by being exposed to a first plasma source of a low-energy and non-thermal plasma.

In an embodiment, the first plasma source provides Oxygen plasma and is set according to a first set of exposure parameters. As noted above, these parameters include, for example, power, frequency, gas flow rate, and time duration. The values of the first set of exposure parameters are determined based, in part, on the type of the substrate. At the end of S220, only desired areas of the surface of the substrate will react with the ink composition. In certain embodiments, S210 and/or S220 are optional. That is, the process disclosed herein can be performed on pre-treated substrates. Such substrates can be pre-treated by a different machine or at a different facility.

At S230, a mask is placed on the treated substrate. In an embodiment, shadow masking is utilized such that a polymeric mask is applied directly to the surface of the treated substrate. In such embodiments, voids (spaces) in the mask define where the ink composition contacts the substrate surface. According to another embodiment, the treated substrate's surface is selectively modified using, for example, photolithographic techniques. According to some embodiments, the substrate includes photoactive functional groups. Thus, once a mask is applied to the substrate, the substrate's surface may be irradiated with any appropriate type of radiation such that only the photoactive groups not covered by the mask are irradiated. This masking technique creates treated and non-treated areas on the substrate. As a result, the treated areas have higher or lower affinity to the components of the ink composition than the non-treated areas.

According to further embodiments, micro-contact printing, chemo-mechanical surface patterning, selective chemical modification, and template assisted patterning or any other appropriate procedure may be utilized for the partial modification of the surface of the substrate. It should be noted that, in certain embodiments, S230 is optional.

At S240, the ink composition is applied on the void areas of the mask. In an embodiment, the ink composition can applied by means including, but not limited to, a drop-casting, spin-coating, spray-coating, immersion, flexography, gravure, inkjet printing, aerosol jet printing, contact imprinting, and the like.

At S250, the substrate including the ink composition is exposed to a second plasma source as determined by a second set of exposure parameters. In an embodiment, the second plasma source provides Argon or Nitrogen plasma. In certain embodiments, the same chamber is used for both the first and second plasma sources. In an optional embodiment, the chamber for the second plasma source is a vacuum chamber. In a further embodiment, the first plasma source may be the same as the second plasma source.

In yet another embodiment, the second plasma source utilized in S250 is atmospheric plasma of inert gas. Exposing the substrate to the atmospheric plasma can be performed using an atmospheric plasma jet, an atmospheric plasma spray, a dielectric barrier discharge, and the like. In all of the above noted embodiments, the second plasma source is of the low-energy and non-thermal plasma.

The second set of exposure parameters include power, frequency, gas flow rate, and time duration. The values of the second set of exposure parameters are determined based, in part, on the type of the substrate 110, the ink composition 130, and/or the means of application.

As a non-limiting example, the values of the second set of exposure parameters may be as follows: the power is between 5 W (watt) and 600 W, the plasma RF frequency is between 50 Hz and 5 GHz, the gas flow rate is between 2 SCCM and 50 SCCM, and the exposure time is between 1 second and 5 minutes.

It should be noted that the plasma RF frequency and the operation power are chosen according to the reduction potential of the metal. Generally, metals with higher reduction potentials require lower plasma RF frequencies and operation powers. The time of exposure is determined according to the metal-cation concentration in the composition, the reduction potential of the metal, and/or the gas flow rate. It is noted that, generally, lower metal-cations concentrations, as well as metals with higher reduction potentials and greater gas flow rates, require a shorter plasma exposure time, since at such conditions the rate of precipitation is higher.

In certain embodiments, S250 may be repeated a predefined number of cycles, and the second set of exposure parameters may be set to different values for each cycle. In an embodiment, the number of cycles may be between 2 and 10. As noted above, the number of cycles determines, in part, the thickness of the metal.

Once the plasma exposure cycle(s) is completed, the substrate may be removed from the chamber. At this point, the ink composition has been converted to a patterned thin metal film, which is adhered to the substrate. As will be discussed herein, the ink composition may be composed of different metal cations, and different contractions thereof. The resulting thin metal film may be comprised of various types of metals and/or alloys. According to some embodiments, the thickness of the thin metal film is between 0.02 μm and 2 μm.

As noted above, the chemical and electrical properties of the patterned thin metal film are determined based on the chemical properties of the composition and the substrate and/or the values of the plasma exposure parameters.

FIG. 3 shows an exemplary and non-limiting block diagram of a machine 300 structured to form thin patterned metal films on substrates according to the various embodiments disclosed herein. That is, the machine 300 can also serve as a printing machine, a fabrication machine, a manufacturing machine, and the like. The machine 300 can be utilized for mass-production of electronic devices including, for example, RFIDs, electronic sensors, integrated electronic circuits, flexible displays, photovoltaic devices, organic field effect transistors, OLEDs, and the like.

According to some embodiments, the machine 300 includes a plasma jet 310, a nozzle 320 coupled to a container 330 containing the ink composition, and a controller 340. The plasma jet 310 is connected to one or more containers 350-1, 350-n that are the sources for the different plasma gas. For example, containers may include Argon Plasma, Oxygen plasma, Nitrogen plasma, and the like. The containers 350 may or may not be part of the machine 300. The plasma jet 310 is a means for dispensing atmospheric pressure plasma. The plasma jet 310 can be replaced by an atmospheric plasma with corona discharges, and dielectric barrier discharges. The movement of the plasma jet 310 is controlled by a moving arm 315.

In certain embodiments, when vacuum (or low-pressure) plasma is utilized, the plasma jet 310 is a replaced by a vacuum chamber controlled by a vacuum pump (not shown).

The nozzle 320 may be any means for applying the ink composition in the container 330 on the substrate 375. The nozzle 330 may be utilized for drop-casting, spin-coating, spray-coating, immersion, flexography, gravure, inkjet printing, aerosol jet printing, contact imprinting, and the like, and the like. The nozzle 330 may be connected to a moving arm 335 to follow a specific pattern.

In certain embodiments, the machine 300 further includes a masking means 360 for applying the mask on the surface of the substrate. The masking means 360 may be also connected to a moving arm 365. The movement of the masking means 360 is controlled by the moving arm 365.

The controller 340 is configured to control the operation of the various components of the machine 300. For example, the controller 340 can set the exposure parameters for the plasma jet 310, select a plasma source, control the injection casting of the composition, control the movement of the various moving arms, and so on.

The controller 340 can be realized as one or more general-purpose microprocessors, multi-core processors, microcontroller, digital signal processors (DSPs), field programmable gate array (FPGAs), programmable logic devices (PLDs), gated logic, discrete hardware components, and the like. The controller 340 may also include machine-readable media for storing software. Software shall be construed broadly to mean any type of instructions, whether referred to as software, firmware, middleware, microcode, hardware description language, or otherwise. Instructions may include code (e.g., in source code format, binary code format, executable code format, or any other suitable format of code). The instructions, when executed by the controller, cause the controller to perform the various functions described herein.

According to various disclosed embodiments, an ink composition for forming thin metal films on substrate is disclosed. The ink composition may be in a form of a solution, dispersion, suspension, gel, or colloid.

In its basic form, the ink composition includes metal cations with at least one type of solvent. According to some exemplary embodiments, the metal cations are M(NO₃)_(n), M(SO₄)_(n), MCl_(n), and HmMCl_(n+m), where “M” is a metal atom (or any appropriate metal alloy) with a valence of “n”, H is hydrogen, NO₃ is nitrate, SO₄ is sulfate, Cl is chloride ,and “m” is a valence of the counter ion. In a further embodiment, the metal cations may be provided in gels, colloids, suspensions, dispersions, organic-inorganic compounds, and so on. According to some exemplary embodiments, the metal cations may be stabilized by counterion, e.g., forming an organometallic complex, such that they are connected by coordinate bonds rather than by ionic bonds.

The solvents that may be used in the ink composition include, but are not limited to, alcohols, water, toluene, dioxane, cyclohexanol, Dimethyl sulfoxide (DMSO), formamides, ethylene glycol, propylene glycol, glycerol, propylene carbonate, and acetonitrile. In some embodiments, the ink composition can contain other additives such as, but not limited to, organic molecules, polymers, conductive polymers, carbon nanotubes (CNT), densifiers, surfactants, and the like. Such additives can be used to change the viscosity.

The ratio between metal containing compound/metal cation and the concentration of solvents is determined based on the type of the metal being used in the solution. The ratio between the solvents in the mixture can be set for different compositions. That is, concentration of the metal cations in the ink composition can be adjusted based on the ratio between the solvent mixture and the metal cations. In some embodiments, the concentration of the metal cations in the ink composition range between 1% wt. and 70% wt. The entire fraction of the solvent in the ink composition is 100% wt., regardless of the number of solvents in the composition.

That is, in a non-limiting embodiment, when one solvent is used, the entire fraction of the solvent is 100% wt. In another embodiment, when a mixture of two solvents is contained ink composition, the first solvent ranges between 75 wt. % and 99 wt. % and a second solvent ranges between 25 wt. % and 1 wt. %, respective of the first solvent. For example, if the first solvent is 75 wt. %, then the fraction of the second solvent is 25 wt. %. In another non-limiting embodiment, when a mixture of three solvents are contained in the ink composition, then the fraction of the first solvent can range between 75 wt. % and 99 wt. %, the second solvent can range between 1 wt. % and 25 wt. %, and the third solvent can range between 1 wt. % and 25 wt. %, with the total percentage of solvent being 100 wt. %.

In yet another embodiment, the solvent mixtures consist of two different types of solvents: a high surface tension solvent and a low surface tension solvent. Examples for a low surface tension solvent include any alcohol-based solvent, while examples for a high surface tension solvent include a DMSO solvent.

According to one embodiment, the ink composition has a viscosity ranges between 0.001 and 0.5 Pa-s (pascal-second). It should be therefore appreciated that with such viscosity the ink composition can be applied or printed on the substrate by means of inkjet printing.

Non-limiting Examples

Following are a few non-limiting examples for ink compositions and forming thin metal films using such compositions.

In a first example, the ink composition includes metal cations AgNO₃ in the concentration of 40 wt. % in water (solvent). This ink composition is silver-based.

Using this ink composition, a silver thin film can be formed on a PET substrate through the following process. A PET substrate is first treated by an Oxygen plasma with the exposure parameters RF frequency, power, and gas flow rate of the Oxygen plasma are respectively set to the following values: 13 MHz, 50 W, and 5 SCCM Oxygen flow rate. The plasma is applied in a vacuum chamber with a low pressure (e.g., 375 Torr) for 5 minutes through a polymer mask with a void area of 2×2 mm to create a hydrophilic pattern.

The silver-based ink composition is then drop-casted on the treated PET substrate, so that the ink distribution on the substrate follows the pattern. Then, the PET substrate with ink composition is placed in a vacuum chamber and exposed to Argon plasma. The chamber is set with the following exposure parameters RF frequency, power, gas flow rate, and time having the values: 13 MHz, 50 W, 3 SCCM gas flow rate, and 1 minute, respectively. The pressure at the chamber is 375 Torr. As a result, a patterned (silver 2×2 mm square) metal film having thickness of 500 nm (nanometer) on top of the PET substrate without any substrate deformation.

As a second example, the ink composition is made of metal cations HAuCl₄ in concentration of 10 wt. % in a mixture of solvents. The mixture includes water and ethanol at a ratio of 90:10 wt. % (water:ethanol). This ink composition is gold-based.

Using this ink composition, a gold thin film can be formed on a silicon substrate through the following process. The silicon substrate is first treated as discussed above with reference to the first example. Here, the exposure time is 5 minutes. Then, the ink composition is drop-casted on the silicon substrate through a polymer mask with a square-shaped void of 5×5 mm to create a square pattern. The silicon substrate with the mask and ink composition are placed in a vacuum chamber and exposed to Argon plasma. The exposure parameters RF frequency, power, gas flow rate, and time are set to 13 MHz, 100 W, 3 SCCM, and 1 minute, respectively. The pressure at the chamber is 375 Torr. As result, a square pattern of a gold metal film having thickness 150 nm is formed on top of the silicon substrate without any substrate deformation.

To thicken the formed film, an additional layer of the ink composition is drop-casted on the silicon substrate through the same polymer mask and placed in the vacuum chamber for another Argon plasma exposure cycle repeated at the same exposure parameters' values as in the first cycle. As a result, the thickness of the formed patterned gold film is 300 nm.

As a third example, the ink composition includes metal cations of Cu(NO₃)₂ in concentration of 5 wt. % in solvent mixture. The solvent mixture include water and DMSO at a ratio of 90:10 wt. % (water:DMSO). This ink composition is copper-based.

In this example, a copper film is formed on a glass substrate covered by PEDOT-PSS polymer. The ink composition is drop-casted on the substrate through a mask with a square-shaped void having an area of 2×2 mm and exposed to Argon atmospheric plasma using a plasma jet. The exposure parameters RF frequency, power, gas flow rate, and time are set 100 kHz, 400 W, and 5 SCCM gas flow rate, and 5 seconds, respectively. As a result, a square-shaped copper film having an area of 2×2 mm and a thickness of 120 nm is formed on the glass substrate.

As a fourth example, an ink composition including metal cations of AgNO₃ at a concentration of 3 wt. % in a solvent mixture of water, 2-propanol, and DMSO at a ratio of 80:15:5 wt. % (water:2-propanol:DMSO). This ink composition is sliver-based.

Using this ink composition, a sliver thin film can be formed on a PET substrate through the following process. The PET substrate treated by atmospheric plasma jet applying Oxygen plasma. The exposure parameters RF frequency, power, gas flow rate, and time are set to 40 kHz, 300 W, 10 SCCM oxygen flow rate, and 10 seconds, respectively. Then, a pattern of hydrophobic lines 500 μm width is created. The ink composition is printed on the PET substrate following the pattern lines using an ink-jet printer. The printed ink lines are exposed to Argon atmospheric plasma using a plasma jet. The exposure parameters RF frequency, power, gas flow rate, and time of the plasma jet are now set to 40 kHz, 300 W, 5 SCCM flow rate, and 15 seconds. As result, a patterned silver metal film with line width of 500 μm and thickness of 70 nm is formed on the silicon substrate.

As a fifth example, the composition includes metal cations AgNO₃ at a concentration of 25 wt. %, CNT at a concentration of 0.02 wt. %, and a solvent mixture. The solvent mixture is of ethanol and water at a ratio of 95:5 wt. % (ethanol:water). The ink composition is printed as a pattern of lines using an ink-jet printer. The printed ink lines are exposed to Argon atmospheric plasma applied using a plasma jet. The exposure parameters RF frequency, power, gas flow rate, and time of the plasma jet are set to 13.54 MHz, 20 W, 5 SCCM argon flow rate, and 5 seconds, respectively. As a result, a pattern of silver metal film with line width of 500 μm and thickness of 200 nm is formed on the PET substrate.

FIG. 4 shows a scanning electron microscope (SEM) image of a silver metal film formed on Silicon substrate according to an embodiment. The film thickness is 150 nm. The plasma used in the second phase is Argon and the exposure time is about 1 minute.

FIG. 5 shows a SEM image of a gold metal film formed on a PET substrate according to an embodiment. The plasma used in the second phase is Argon with exposure parameters RF frequency, power, gas flow rate, and time of the plasma jet set to gold film: 13.54 MHz, 5 SCCM argon flow, 30 W, 1 minute, respectively. The formed gold metal film having thickness is 200 nm.

The embodiments have been described in detail referring to the above examples. It should be appreciated that the disclosed embodiments are not limited to the examples described above, and details of the various embodiments may be variously modified.

It should be understood that any reference to an element herein using a designation such as “first,” “second,” and so forth does not generally limit the quantity or order of those elements. Rather, these designations are generally used herein as a convenient method of distinguishing between two or more elements or instances of an element. Thus, a reference to first and second elements does not mean that only two elements may be employed there or that the first element must precede the second element in some manner. Also, unless stated otherwise a set of elements comprises one or more elements. In addition, terminology of the form “at least one of A, B, or C” or “one or more of A, B, or C” or “at least one of the group consisting of A, B, and C” or “at least one of A, B, and C” used in the description or the claims means “A or B or C or any combination of these elements.” For example, this terminology may include A, or B, or C, or A and B, or A and C, or A and B and C, or 2A, or 2B, or 2C, and so on.

All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the principles of the disclosed embodiment and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions. Moreover, all statements herein reciting principles, aspects, and embodiments of the disclosed embodiments, as well as specific examples thereof, are intended to encompass both structural and functional equivalents thereof. Additionally, it is intended that such equivalents include both currently known equivalents as well as equivalents developed in the future, i.e., any elements developed that perform the same function, regardless of structure. 

What is claimed is:
 1. A method for forming a thin patterned metal film on a substrate, comprising: applying an ink composition on a pre-treated surface of the substrate, wherein the ink composition includes at least metal cations; and exposing at least the applied ink composition on the substrate to a low-energy plasma, wherein the low-energy plasma is operated according to a first set of exposure parameters.
 2. The method of claim 1, wherein the substrate is any one of: an organic substrate, a ceramic substrate, a silicon substrate, an inorganic substrate, a hybrid organic-inorganic substrate, and a glass substrate.
 3. The method of claim 1, wherein the substrate is any one of: a polyethylene terephthalate (PET) substrate, a polyimide substrate, and a polyethylene naphthalate (PEN) substrate.
 4. The method of claim 1, wherein the low-energy plasma is an inert gas plasma.
 5. The method of claim 4, wherein the inert gas plasma includes at least any of: Argon plasma and Nitrogen plasma.
 6. The method of claim 1, wherein the low-energy plasma is any of: an atmospheric plasma and a low-pressure plasma.
 7. The method of claim 4, wherein the first set of exposure parameters includes at least one of: radio frequency (RF), power, gas flow rate, and exposure time.
 8. The method of claim 7, wherein the RF frequency is between 50 Hz and 5 GHz, inclusive.
 9. The method of claim 7, wherein the power is between 5 watts (W) and 600 W, inclusive.
 10. The method of claim 7, wherein the gas flow is between 2 standard cubic centimeters per minute (SCCM) and 50 SCCM, inclusive.
 11. The method of claim 7, wherein the exposure time is between 1 second and 5 minutes, inclusive.
 12. The method of claim 1, wherein applying the ink composition is performed by means including at least any of: drop-casting, spin-coating, spray-coating, immersion, flexography, gravure, inkjet printing, aerosol jet printing, and contact imprinting.
 13. The method of claim 6, wherein exposing at least the applied ink composition on the substrate to the low-energy plasma further comprises: placing the substrate in a vacuum chamber.
 14. The method of claim 6, wherein exposing at least the applied ink composition on the substrate to the low-energy plasma further comprises: using any of an atmospheric plasma jet and an atmospheric plasma spray.
 15. The method of claim 1, further comprising: applying a mask having a void area on the pre-treated surface of the substrate; and applying the ink composition in the void area of the mask, wherein the void area is patterned.
 16. The method of claim 1, further comprising: repeating the exposure of the substrate to the low-energy plasma for predefined number of cycles, wherein at least one exposure parameter of the first set of exposure parameters is set differently at each cycle.
 17. The method of claim 1, further comprising: treating the surface of the substrate to create the pre-treated substrate.
 18. The method of claim 17, wherein treating the surface of the substrate further comprising: cleaning the substrate; exposing the substrate in the plasma chamber to a second low-energy plasma according to a second set of exposure parameters.
 19. The method of claim 1, wherein the ink composition is at least a solution.
 20. The method of claim 19, wherein the ink composition further comprises any of: at least one solvent and a solvent mixture.
 21. The method of claim 20, wherein the metal cations are selected from the group consisting of: M(NO₃)_(n), M(SO₄)_(n), MCl_(n), and H_(m)MCl_(n+m), wherein “M” is a metal atom with a valence of “n”, H is hydrogen, NO₃ is nitrate, SO₄ is sulfate, Cl is chloride, and “m” is a valence of a counter ion.
 22. A substrate printed with a patterned thin metal film using the method of claim
 1. 23. A machine for forming a thin patterned metal film on a substrate, comprising: a container adapted to contain an ink composition, wherein the ink composition includes at least metal cations; a nozzle adapted to apply the ink composition on a pre-treated surface of the substrate; a plasma applicator adapted to expose at least the ink composition applied on the substrate to a low-energy plasma operated according to a first set of exposure parameters; and a controller configured to control the operation of the nozzle and the plasma applicator.
 24. The machine of claim 23, wherein the substrate is any one of: an organic substrate, a ceramic substrate, a silicon substrate, an inorganic substrate, a hybrid organic-inorganic substrate, and a glass substrate.
 25. The machine of claim 23, wherein the substrate is any one of: a polyethylene terephthalate (PET) substrate, a polyimide substrate, and a polyethylene naphthalate (PEN) substrate.
 26. The machine of claim 23, wherein the low-energy plasma is an inert gas plasma.
 27. The machine of claim 26, wherein the inert gas plasma includes at least any of: Argon plasma and Nitrogen plasma.
 28. The machine of claim 23, wherein the low-energy plasma an atmospheric plasma, and the plasma applicator is any of: an atmospheric plasma jet and an atmospheric plasma spray.
 29. The machine of claim 23, wherein the low-energy plasma is a low-pressure plasma and the plasma applicator is a vacuum chamber.
 30. The machine of claim 23, wherein the first exposure parameters includes at least one of: radio frequency (RF), power, exposure time, gas flow rate, and exposure time.
 31. The machine of claim 30, wherein the RF frequency is between 50 Hz and 5 GHz, inclusive; wherein the power is between 5 watts (W) and 600 W, inclusive; the gas flow is between 2 standard cubic centimeters per minute (SCCM) and 50 SCCM, inclusive; and the exposure time is between 1 second and 5 minutes, inclusive.
 32. The machine of claim 23, wherein the nozzle is adapted to apply the ink composition by at least any of: drop-casting, spin-coating, spray-coating, immersion, flexography, gravure, inkjet printing, aerosol jet printing, and contact imprinting.
 33. The machine of claim 23, further comprising: means for applying a mask on the pre-treated surface of the substrate, wherein the nozzle is adapted to apply the ink composition in a void area of the mask, wherein the void area is patterned.
 34. The machine of claim 23, wherein the controller is further configured to: cause repetition of the exposure of the substrate to the low-energy plasma for a predefined number of cycles, wherein at least one parameter of the first set of exposure parameters is set differently at each cycle.
 35. The machine of claim 23, wherein the controller is further configured to: cause the plasma applicator to pre-treat the surface of the substrate by exposing the substrate to a second low-energy plasma according to a second set of exposure parameters.
 36. The machine of claim 23, wherein the ink composition is at least a solution.
 37. The machine of claim 36, wherein the ink composition further comprises any of: at least one solvent and a solvent mixture.
 38. The machine of claim 36, wherein the metal cations are selected from the group consisting of: M(NO₃)_(n), M(SO₄)_(n), MCl_(n), and HmMCl_(n+m), wherein “M” is a metal atom with a valence of “n”, H is hydrogen, NO₃ is nitrate, SO₄ is sulfate, Cl is chloride, and “m” is a valence of a counter ion. 